This invention is directed primarily to heat pump systems which are applied to heating and air conditioning loads of the environment in the living spaces of buildings. As used herein, the term air conditioning means the adjustment of the temperature and humidity in the living space to selected comfortable norms when the outside environment and particularly the ambient temperature, is either too high or too low for comfort. However, many of the objectives and concepts of this invention also have application to other types of thermal loads. Therefore the term "load" as used herein while specifically in the context of air conditioning, may be interpreted broadly to apply to other thermal loads by those familiar with heating and cooling technology.
It is well recognized that air conditioning and heat pumping thermal systems require a heat source from which the heat load may be transferred in the heating mode. In recent time and particularly in connection with air conditioning activity, efforts have been directed to the convenient economical use of ambient outside air as the heat sink for the cooling load, and also as the heat source in the heating or heat pumping mode.
Most heat pumps in commercial use, and particularly with respect to a residential application, are of the vapor compression type wherein the refrigerant gas, usually freon R-22, is compressed, condensed, and evaporated to lower pressure in an evaporator that absorbs heat. In the cooling mode of operation the compressed vapor condensing means (an outdoor heat exchanger) is located in contact with the ambient outside air where the heat of compression is transferred to the ambient air. The condensed refrigerant is expanded or evaporated in a means for exchanging heat with the heat load of a living space.
In the heating mode, the system is reversed and the indoor heat exchanger receives the compressed hot gas which is condensed by heat exchange with the heat load of the living space, after which the gas is expanded in heat exchange with the ambient air, thereby absorbing heat from the ambient outside air. By this means heat is "pumped" from the ambient outside air into the living space.
In these systems mechanical energy is required to compress the refrigerant vapor. In the most common typical and conventional system refrigerant vapor is compressed in a rotating or reciprocating compressor which is frequently driven by an electric motor. In those systems an external source of electrical power input is required.
In other circumstances, the compressor is driven by an internal combustion engine or other form of motive power, but inside and outside fans and the engine starter are driven by electric motors connected to an outside source of power. Such engine driven systems can be more efficient, and in them, it is mechanically desirable to eliminate the need for a source of external electrical power. This is accomplished by connecting and driving an electrical generator as an auxiliary source of electrical energy for the various auxiliary components of the system. Such components may include motors to start the engine and drive the fans, to move the air, as well as pumps to move other fluids through the system.
The co-generation of electrical energy in these systems is attendant with various problems such as, maintaining constant electrical output when the mechanical motive power varies according to the refrigeration and/or heat load on the system.
In these engine driven heat pump systems with auxiliary generators, it has been found most efficient that the generator be of the induction motor type and that the output for the auxiliary components be alternating current, typically 60 cycle, as commonly provided from other sources. In order to provide 60 cycle alternating current power, it is necessary that the generator be operated at substantially constant speed.
It will be well recognized that the heating and cooling load in air conditioning systems will vary over a wide range of conditions.
At one heating extreme the heat load will be very high when the ambient outside temperatures are very low. On the other hand, the cooling load will be very high when the outside ambient temperatures are elevated to a high temperature.
An additional problem with the operation of heat pumping systems of the "air source" type is that when the outside temperature is very low it is difficult to efficiently operate the refrigerant gas compressor as the refrigerant gas is very thin at low temperature and therefore the load on the compressor is drastically reduced, in many cases to the point where auxiliary heat is required.
For these reasons when the compressor is driven by an internal combustion engine the load on the engine will vary dramatically with the compressor load. Consequently, engine throttle control and speed control are an important factor.
The combination of the various variables in the operation of the engine driven heat pump system are further compounded when the system is used to drive an auxiliary generator that is desirably operated at constant speed.
This invention is directed to an apparatus providing for the interconnection and cooperation of the various components of the system in a manner to provide optimum solution to the problems set forth above.
In the past others have directed their attention to some of the facets and requirements in providing an efficient system.
For instance, U.S. Pat. No. 3,691,784--Ruff et al. discloses a variable capacity mechanical refrigeration system for heat pump or cooling operation with a variable speed centrifugal compressor motor drive that uses an electronic frequency conversion apparatus which is sensitive to and controlled by discharge or suction pressure of the compressor. In this patent, the compressor is driven by an electric motor of the squirrel cage induction type.
More pertinently, U.S. Pat. No. 3,559,724--W. H. Wilkinson, who is also the inventor of this invention, discusses a means of controlling the speed of the compressor output by means of a planetary differential as a means for adjusting the engine shaft power split between the generator and the compressor in response to changing conditions at the evaporator, i.e. at the load, by using a hydrostatic variable speed device between the engine and the compressor. In this previous invention, the compressor speed is directly controlled by the hydrostatic device while the differential planetary limits the amount of power actually transmitted through the hydrostatic device.
Whereas a hydrostatic variable speed device can stall one output (the compressor) as it maintains the generator at a controlled speed, a hydrostatic device is too expensive and requires too careful maintenance for residential and small commercial applications. Traction type continuously variable transmissions (CVT) can be reliable and inexpensive but cannot "stall" one output (infinite gear reduction). Belt driven CVT's generally provide continuous ratios from about 1:2 speed increase to 2:1 speed decrease. This invention involves locating the CVT between the driving unit (the engine) and the generator so that the compressor output can be indirectly defined as a difference which can go to zero. This unique CVT location allows a traction type CVT to provide control functions similar to those of the hydrostatic system, but without the disadvantages of a hydraulic system.